1. Field of the Invention
This invention generally relates to automated mechanical positioning devices and more particularly to a positioning apparatus in three dimensions.
2. Description of the Related Art
Conventional three dimensional positioning devices typically have an X axis stage which is movably mounted on a fixed base surface with its servomotor fastened to the base surface, driving a screw and nut on the screw which is in turn fixed to the X axis stage. As the screw rotates, the nut moves in the X direction and carries with it the X axis stage. The Y-axis stage motor may also be fixedly mounted on the base surface, i.e. decoupled from the X stage. In this case the Y stage may be directly above the X axis stage and may be mounted on two rollers on either side of an elongated bar or "Y direction bar" aligned along the X axis. The Y axis motor is mounted on the base and drives a screw with a nut connected to the "Y" direction bar. The Z axis servo motor is typically mounted on the Y stage and operates a bell crank to move a component being positioned, such as a probe, up and down along a Z axis.
Alternatively, as shown in FIG. 1, the XYZ stage 10 for positioning a bond tool 12 in three dimensions has an X axis motor 14 fixed to a base 16. Slidably mounted on base 16 is an X stage 18 which is moved back and forth on the base 16 in the X direction 19 by the X axis motor 14 through a nut on a screw (not shown). The Y axis motor 20 is fastened to the X stage 18 and drives a Y axis stage back and forth along the Y direction 24 over the X stage. The Z axis drive motor 26 is mounted on the Y stage 22 and operates through a linkage 28 to raise and lower the bonder 12 in the Z direction 30, thus providing XYZ positioning of the bonder 12 with respect to the base 16.
A major problem with the above designs is that both the X and Y stage motors have a tremendous inertial mass to overcome during movement. The X axis motor 14 must move the entire assembly including the Y and Z motors and X, Y, and Z stage components. The Y motor must move the Z motor in addition to the Y stage. This is not a problem in many applications. However, transit time becomes a significant problem when indexing must be done quickly and frequently. The response time of a computer controlled stage such as the ones above described is largely limited by this inertial mass problem. The positioning of a bonder in semiconductor manufacturing today is fast becoming a major contributor to the overall processing time. Reducing processing time would mean higher throughputs and increased productivity which translates to lower cost. Consequently there is a need for a XYZ stage design which minimizes inertial mass dependent movements and a design in which the bonder or other component being positioned can be more rapidly positioned than is currently available with conventional machines.